Are there HTML5 desktop app frameworks (like Titanium or Adobe AIR) that run on V8 or Rhino instead of JavaScriptCore?

Question

Our product, a desktop app, is composed of a ton of HTML5 and JavaScript together with a thin platform-specific layer that is basically a WebKit shell. Since this is much the same strategy as a framework like Appcelerator Titanium, and we waste way too much effort on this custom WebKit shell code, we were hoping to switch to Titanium or a similar framework to handle that for us.

However, such a switch would be much more compelling if we could pick up a nice modern JavaScript engine in the process. Like Titanium, we're currently on JavaScriptCore, which sucks (they still don't have Function.prototype.bind!). We'd take either V8, for speed and modernity, or Rhino, for yummy JavaScript 1.7/ECMAScript Harmony features.

Does anyone know of a framework for building desktop apps with HTML5 that uses either of these engines? Or some way of making either work with Titanium that will be very little effort? I saw the v8_titanium and rhino_titanium projects on GitHub, but see no mention of them anywhere else, or any documentation on how to use them. And the Adobe AIR WebKit page has nothing encouraging either.